engine vs battering ram

engine and battering ram both are nouns.

Word	Noun	Adjective	Verb	Adverb
engine	Yes	No	No	No
battering ram	Yes	No	No	No

As nouns, battering ram is a hyponym of engine; that is, battering ram is a word with a more specific, narrower meaning than engine:

engine: an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
battering ram: a ram used to break down doors of fortified buildings

Other hyponyms of engine include catapult, ballista, bolt thrower.

engine (noun)	battering ram (noun)
motor that converts thermal energy to mechanical work	a ram used to break down doors of fortified buildings
a wheeled vehicle consisting of a self-propelled engine that is used to draw trains along railway tracks
an instrument or machine that is used in warfare, such as a battering ram, catapult, artillery piece, etc.
something used to achieve a purpose